1. Field of the Invention
The invention relates to a disposable hypodermic syringe and needle combination designed to eliminate the hazard of accidental needle sticks. In particular, the invention relates to an apparatus for and method of retracting a needle into a syringe after injection so that the needle cannot be forced back out of the syringe.
2. Background Art
The disposal of contaminated hypodermic syringe needles has been and continues to be a major health concern. The Medical Waste Tracking Act of 1988 disclosed that injuries caused by discarded hypodermic needles are the cause of new human immunodeficiency virus (HIV) and hepatitis virus transmittals each year. Those at greatest risk are nurses, emergency medical personnel, medical waste handlers, dental assistants, physicians and dentists. An estimated 25,000 medical waste injuries are predicted annually, resulting in several deaths.
Disposable hypodermic syringes presently in use are distributed in two forms. One form of disposable hypodermic syringe has the hypodermic needle attached to the syringe and the other form requires that the needle be attached to the syringe just before use. In the operation of a conventional disposable hypodermic syringe, the procedure for preparing the syringe/needle assembly for injection is as follows: 1) the plunger is fully depressed into the syringe; 2) the needle is inserted into a vial containing the injectable material; 3) the plunger is withdrawn to a point indicating the prescribed volume of injectable material; 4) the syringe is positioned to place the needle in an upright position; 5) the plunger is depressed to the point where a drop of the injectable material emerges from the lumen of the needle in order to force trapped air out of the syringe; 6) the needle is inserted into the subject; and 7) the plunger is fully depressed, forcing the injectable material through the needle and into the subject.
After the hypodermic needle pierces the skin and is withdrawn, the needle requires disposal. Various inventions have attempted to address this problem including 1) procedures for the disposal of hypodermic needles; 2) designs for incorporation of a sheath that covers the needle abler the needle is used; and 3) designs for retracting the needle into the syringe after use. However, these procedures must be carried out properly and consistently by all persons involved in the disposal of hypodermic needles and are not foolproof. Although syringes with sheaths are presently being used, these types of syringes are more expensive due to unnecessary complexity, greater production costs and greater material requirements.
In addition to greater production costs and material requirements, an even more serious and potentially fatal problem exists in the design of most disposable syringes with retractable needles, which is the possibility of injecting air into a subject.
In previous designs for syringes with retractable needles, the needle is partially fixed inside the syringe to a depth sufficient for the needle to be captured by the plunger and subsequently withdrawn. This means that when the syringe is filled, the plunger cannot be fully depressed, to avoid premature capture of the needle. Consequently, there is always a space filled with air inside the syringe. Dispelling the air within the syringe is problematic. Because the needle is partially fixed inside the syringe, the air bubble cannot be fully driven out. The air bubble floats to the highest point in the syringe, precluding the possibility of positioning the air bubble at the inner opening of the needle, from where it can be expelled. However, in the course of injecting the material within the syringe into the subject, the plunger is fully depressed, expelling the trapped air bubble into the subject, with potentially fatal consequences.
Therefore, there exists a need for a disposable hypodermic syringe with a retractable needle, designed such that any air bubble in the syringe can be fully expelled prior to injection.